Regarding VC-1 playback on the NVidia Shield: Most of what's been stated is correct: It has hardware support for VC-1 decoding. It works in the 7.X series of OSes for Shield. The 8 release broke it and now it's only decoded in software, which is on the CPU.
However, if you subscribe to the hotfix channel, it works again. Great right? Well... not so much. The hotfixes are "not supported". They break other stuff. I've read threads about them breaking HDMI sync in some cases. The worst part though, is that once you sign up for hotfixes, by registering your serial number, you can't ever unsubscribe. So you'll be offered hotfixes until they stop producing them. I think that's once a week for the next few years.
Jmone: If VC-1 works "perfectly" for you, one of a few things is going on (I think):
A. You have an OS that supports VC-1 in hardware. Maybe you have an 8 series hotfix release installed.
B. Your testing did not include a long enough section or a difficult enough movie. I have about 50 VC-1 titles from BluRay that are in MKV containers. A few of them play seemingly fine for a minute or two. Then you start to notice jumpy, jerky behavior. It's kind of subtle on these titles. On other titles, it's immediately obvious and awful. It's unwatchable. As an example, "The Breakfast Club" is really bad. The audio is even out of sync on that one.
C. MO Media is magical and does software VC-1 decoding better than anything else.
I should go try MO Media assuming it's free.
Regarding frame rate matching: Kodi will frame rate match, no problem, on the Shield. It's just a setting. There's no need to use an external player.
Thanks everyone. Special thanks to jmone who actually did testing on my behalf. I appreciate it.
Brian.